Relative abundance of diatoms in surface sediments of Lake Lama

The patterns of spatial variation of diatom assemblages from surface sediments in Lake Lama were quantified using a combined approach of ordination and geostatistics. The aims were (i) to estimate the amount of variation between diatom assemblages within the lake, (ii) to model the spatial variability of the diatom assemblages and their diversity, and (iii) to map the diatom distributions in the lake. A correspondence analysis (CA) separated the diatom assemblages into a planktonic and a periphytic group. Rheophilic taxa were found within the periphytic group. Variogram analysis showed that only the sample scores of the first CA axis and the Shannon diversity index were spatially structured. The range of spatial correlation was estimated to be 55 km for both variables. The diversity and, to a lesser extent, the sample scores had considerable small-scale variability of about 20 and 3%, respectively. Estimates of the first component of the CA and the Shannon index were derived using block-kriging. The maps of the estimates provided a basis for partitioning Lake Lama according to the spatial structures into an eastern and a western basin, a north–south connection between the basins, and a north–south directed tip at the far eastern end. It was shown that variation in diatom assemblages is mainly spatially structured at the catchment scale and that there is a considerable amount of variation at smaller scales. According to the modeled spatial distribution, the assemblages are most likely affected by the lake size, morphology, and the water and nutrient input introduced by rivers. This has to be taken into account when paleolimnological interpretations are drawn from records of complex lake systems like Lake Lama.

本研究采用排序分析与地统计学相结合的方法，对拉玛湖（Lake Lama）表层沉积物中的硅藻组合空间变异模式开展了定量分析。研究目标包括：(i) 评估湖内不同硅藻组合间的变异程度；(ii) 构建硅藻组合及其多样性的空间变异模型；(iii) 绘制湖内硅藻分布图谱。通过对应分析（Correspondence Analysis, CA），可将硅藻组合划分为浮游类与周丛类两个类群，周丛类群中包含嗜流类群。变异函数分析结果显示，仅第一CA轴的样本得分与香农多样性指数（Shannon diversity index）呈现空间结构特征。二者的空间相关范围均被估算为55 km。多样性指数以及样本得分（后者的小尺度变异程度相对更低）分别存在约20%与3%的显著小尺度变异。研究采用块克里金（block-kriging）方法对第一CA轴分量与香农多样性指数进行了空间估算。基于估算结果绘制的分布图可将拉玛湖依据空间结构划分为东、西两个湖盆，两湖盆间存在南北向连通通道，且在湖体最东端存在一处南北走向的尖端区域。研究表明，硅藻组合的空间变异主要以流域尺度为主，同时在更小尺度上仍存在大量变异。基于模拟得到的空间分布模式，硅藻组合很可能受到湖体规模、形态以及河流输入的水体与营养盐的共同影响。在基于拉玛湖这类复杂湖系的沉积记录开展古湖沼学解释时，需将该影响因素纳入考量。